[phicoh]

I'm curious, when was it right to left?

In computer speak, the way we write numbers in English is 'big endian'. We write the most significant digit first.

The most common 'little endian' system is postal addresses, where we start with the smallest unit (name) then in, some cases, house number, street, city, country.

Note that roman numerals are commonly written in big ending way. So this practice is very old.

[NeedMoreTea]

Yet historically English numbers were little endian, base twenty: "four and twenty" etc. Base 20 comes from Celtic roots I think, so perhaps other European languages have a similar history too.